Purple Door

Purple Doors are doors that can be opened by a beam using an electrical, oscilating beam, the Wave Beam. They are found only in Metroid Prime. The purple color is actually the color of a force field covering the door. After shooting a purple colored door, the energy covering it will disrupt and dissipate, allowing Samus to enter the next room.

In Metroid Prime 3: Corruption, there is no purple door. However, the key of the map mentions a purple "Grapple Voltage Door" despite the lack of one in the game. Instead, there are terminals with a purple color.

In Metroid: Samus Returns, there are two purple door-blocking creatures: the Taramarga, which uses a large rock as an obstruction that can be bypassed with the Wave Beam; and the Gigadora, a three-eyed creature that can only be destroyed with simultaneous shots to each of its eyes which the Spazer Beam can accomplish.